1. Field of the Invention
This invention relates to electrical conductors and more particularly to electrical conductors housed in an extruded plastic material which is arranged to permit the easy folding thereof.
2. Background Prior Art
Electrical conductors such as cables and electrical cords are typically coated with rubber or plastic and are well known in the art. In the basic construction of such cables or wires, the conductor usually is the only metallic part and can be a single or multiple strand surrounded by an enveloping jacket which is usually a unitary plastic composition. Some cables or cords may have a built up construction of two or more plastic or rubber layers extending therealong.
Such electrical cords or conductors are thick and usually found attached to computers, between computers and peripheral devices such as printers or monitors, appliances or tools and portable equipment. Many appliances are purchased with these electric cords or cables neatly wound in a bundle with a tie or packaged with plugs at both ends. With computers and peripheral equipment the cables have male and female ends and are bound together with ties. Removal of the tie causes unfolding of the cable or cord. When it is desired to re-bundle or re-coil the electric cord or cable, it is often difficult to do so in a neat or uniform manner. This is especially true of cables associated with computers and most owners simply maintain a mess of tangled wires hidden behind a desk.
Such hindrance to the neat and uniform re-folding of a power cord or cable is due to the unitary form of layering built up about the central conductive metallic core or cores.
An object of the present invention is to overcome the disadvantages of the prior art.
A further object of the present invention to provide an electric power cable or cord which is easily re-foldable and formed into a bundle so as to permit easy re-wrapping or folding thereof.
Another object of the present invention is to provide an electric power cable or cord which is easily manufactured and economically produced with minimal increased cost for the manufacturer.
Yet another object of the present invention is to provide an electrical conduit for a cable which minimizes kinking and undesired twisting by using a strain relief section.
The present invention relates to the manufacture of an electrical power cable or cord having uniquely flexible properties, for example differential stiffness, in different sections along its length. The cable is to be utilized in conjunction with home appliances and portable equipment. A power cable or conduit made utilizing the principles of this invention has a generally stiff section alternating with a flexible section with a unique transition section of controlled length in repeating sequence axially along the length of the cord. The merging of the two materials forming the stiff sections and the flexible sections are smooth and gradual to eliminate any buckling and kinking that might otherwise occur at abrupt joints between two materials of different stiffness. The average length of a transition section in such a power cable or conduit is about 0.1 to 20 inches, preferably about 0.2 to 10 inches.
The cable of the present invention may be made by means of a co-extrusion process with a co-extrusion head. The co-extrusion head is arranged to minimize volumes of all the flow channels therewithin. Such a flow head is shown and described in my U.S. Pat. Nos. 5,533,985 and 6,135,992, both of which are incorporated herein by reference, in their entirety. The present invention thus provides for the production of an extruded power cable or conduit with an electrical conductor being co-extruded using several thermoplastic resins of varied thicknesses which can be automatically fed into the co-extrusion head and precisely synchronized fashion to produce a power cable or conduit having different resins or resin combinations in different longitudinal sections of the cable, always with gradual transitions from one to the other in short transition sections. A unique characteristic of the invention is the gradual change and the controlled shorter length of the transition section between a soft flexible portion and a stiff portion of the extruded material about the conductive core of the cable, preferably in a wedge-in configuration. A wedged-in construction of the transition section of the power cable or conduit can comprise a layer of one material forming a wedge shaped profile extending into another material. The construction is such that the wall gradually changes from a first material to a second material having less stiffness so that the material gradually changes from a material of a predetermined stiffness to a one of less stiffness to form an unbroken wall of insulating material. This construction is formed by a skewing volume which is not overly short and with a viscosity of the wedging material or resin not overly high when compared with the resin into which it is wedged.
In forming a power cable or conduit of the present invention, one material or resin is always gradually combined with another material in the transition zone with some aspects of the resin forming a wedge structure circumferentially about the central conduit. In other configurations, the wedge may be in the form of a gradually fitting layer or in gradually changing the shapes such as multiple spear points. This wedge construction forms an extremely secure virtually unbreakable joinder between two resins because of the large surface area that also forms the region of greater flexibility of the resin thereof.
The present invention thus comprises an elongated cable for the communication of electrical power from a source to an electrically powered device. The cable comprises an elongated electrical conductor, a first insulating material arranged about a first linear segment of the elongated electrical conductor and a second insulating material arranged about a second linear segment of the elongated electrical conductor. The first and second insulating materials are different from one another. The first and second insulating materials may be thermoplastic resins. The first linear segment and the second linear segment are adjacent one another along the elongated electrical conductor. The elongated electrical conductor has a plurality of first and second segments disposed along its longitudinal length, each of the segments being of different stiffness. The first and second segments are arranged in an alternating sequence with one another along the elongated electrical conductor. The first and second segments may have a transition zone therebetween of increasing flexibility in its longitudinal direction or may have a transition zone therebetween of decreasing flexibility in its longitudinal direction.
The invention also includes a method of manufacturing an insulated electrical power cable with an insulator extruded therearound of alternating flexibility along its length. The method comprises the steps of arranging an extrusion head to receive a conductive wire therethrough, attaching a first and a second insulating material extruder in communication with the head, the first and second insulating material extruders each extruding insulating material of different flexibility from one another when the insulating material is cured, directing the conductive wire through the head and alternatingly extruding the first and second insulating materials to enclose alternating segments of the length of the conductive wire as the conductive wire is drawn from the head. The method includes the steps of tapering the first and second insulating materials with respect to one another in a transition zone juncture between the alternating segments of insulating materials. The insulating segment material may comprise thermoplastic resins.